A compound having the formula: ##STR2## (hereinafter referred to as Compound (I)) is disclosed in U.S. Pat. No. 4,576,934 (hereinafter referred to as Reference (a)).
Compound (I) has excellent characteristics such that it gradually reduces the blood pressure without substantially affecting the heart rate, and yet such action lasts for a long period of time. [Lecture No. A-9, delivered on Oct. 13, 1985 at the 73rd Meeting of Kanto Division of Nippon Pharmacological Association (hereinafter referred to as Reference (b))]
Compound (I) has three asymmetric carbon atoms, and it should have optical and stereo isomers. However, the above-mentioned References (a) and (b) disclose nothing on such isomers.